Semi-trailer drag is a well known phenomenon and there are numerous patents aimed at minimizing its effects. Reviewed drag reducers include U.S. Pat. Nos. 2,569,983; 2,737,411; 3,425,740; 4,006,932; 4,116,482; 4,142,755; 4,236,745; 4,601,508; 4,682,808; 4,702,509; 4,978,162; 5,058,945; 5,236,347; 5,498,059; 5,823,610; 6,092,861; 6,309,010; 6,409,252; 6,467,833; 6,595,578; and Patent Application Publication US 2003/0205913 A1.1. Because of the large number of miles driven by the U.S. tractor-trailer trucking fleet, a widely adopted semi-trailer drag reducer, even of small efficiency, would yield significant industry cost savings, reduced carbon footprint, and reduced dependence on imported and domestic fossil fuels.
Tractor airfairings (i.e., front cab roof mounted devices) are now almost universally installed on American long-haul tractor-trailers, but there is no corresponding acceptance of rear-mounted drag reducers. Tractor airfairings are configured and installed in many shapes and sizes, presumably of different aerodynamic efficiencies. Similarly, prior artwork of patented drag reducers has varied shapes and sizes, but none of these drag reducers are seen on American Interstate highways. Aerodynamic efficiency, apparently, is not the primary reason for lack of industry acceptance of drag reducers.
There are three obvious properties that any drag reducer must include, in addition to providing an aerodynamic benefit, to be commercially successful.
First, the drag reducer must be installed at minimum cost. Costs are recovered a gallon of fuel saved at a time. To achieve a viable payback, materials must remain cost effective.
Second, a successful design must be robust and vandal resistant. Complicated machinery or electronics, air scoops or pumps, and moving parts of all kinds must be minimized to avoid costly maintenance. While tractors rarely sit idle, semi-trailers frequently sit empty in all types of environments, sometimes for extended periods. Components of any perceived significant value are subject to extreme weather conditions and would be prey to vandals.
Third, the time and effort required to deploy or collapse and stow the drag reducer must be minimized. A single person (the driver) typically opens and closes the semi-trailer doors while standing on the road surface. The doors must be able to rotate a full 270 degrees and lay flat as semi-trailers are routinely backed into enclosed docks for loading and unloading.
When an aerodynamically designed drag reducer can be installed economically, is of robust design, and is able to be deployed and stowed quickly, only then will industry acceptance be assured. The Umbrella Semi-Trailer Drag Reducer uniquely satisfies these demands.